Biomedical subjects

Ken Cheng

Publications and source records attributed to Ken Cheng.

13 recordsLinked to original sources

PubMed2006

Small-scale spatial cognition in pigeons.

Roberts and Van Veldhuizen's [Roberts, W.A., Van Veldhuizen, N., 1985. Spatial memory in pigeons on the radial maze. J. Exp. Psychol.: Anim. Behav. Proc. 11, 241-260] study on pigeons in the radial maze sparked research on landmark use by pigeons in lab-based tasks as well as variants of the radial-maze task. Pigeons perform well on open-field versions of the radial maze, with feeders scattered on the laboratory floor. Pigeons can also be trained to search precisely for buried food. The search can be based on multiple landmarks, but is sometimes controlled by just one or two landmarks, with the preferred landmarks varying across individuals. Findings are similar in landmark-based searching on a computer monitor and on a lab floor, despite many differences between the two kinds of tasks. A number of general learning principles are found in landmark-based searching, such as cue competition, generalization and peak shift, and selective attention. Pigeons also learn the geometry of the environment in which they are searching. Neurophysiological studies have implicated the hippocampal formation (HF) in avian spatial cognition, with the right hippocampus hypothesized to play a more important role in the spatial recognition of goal locations. Most recently, single-cell recording from the pigeon's hippocampal formation has revealed cells with different properties from the classic 'place' cells of rats, as well as differences in the two sides of the hippocampus.

Animals↗

PubMed2006

Longitudinal gains in self-regulation from regular physical exercise.

OBJECTIVES: The purpose of the present study was to test whether the repeated practice of self-regulation could improve regulatory strength over time. METHOD: Regulatory performance was assessed at baseline, then at monthly intervals for a period of 4 months using a visual tracking task. Perceived stress, emotional distress, self-efficacy and general regulatory behaviour were assessed by questionnaire. Following a 2-month control phase, participants entered a 2-month self-regulation programme designed to increase regulatory strength: a programme of regular physical exercise. RESULTS: Relative to the control phase, participants who exercised showed significant improvement in self-regulatory capacity as measured by an enhanced performance on the visual tracking task following a thought-suppression task. During the regulatory exercise phase, participants also reported significant decreases in perceived stress, emotional distress, smoking, alcohol and caffeine consumption, and an increase in healthy eating, emotional control, maintenance of household chores, attendance to commitments, monitoring of spending and an improvement in study habits. The control phase showed no systematic changes in performance on the visual tracking task across sessions. Reports of perceived stress, emotional distress and regulatory behaviours were also stable across sessions. CONCLUSIONS: The uptake and maintenance of an exercise programme over a 2-month period produced significant improvements in a wide range of regulatory behaviours. Nearly every major personal and social problem has some degree of regulatory failure. The idea that the capacity for self-regulation can be improved is therefore of vast practical importance.

Adult↗

PubMed2006

Determinants of range effects in face recognition.

The effects of test stimulus range on generalization gradients in humans were assessed for discriminations between faces that varied in brightness, faces that varied in orientation in the picture plane, and morphed faces. In Experiment 1, significant range effects, predicted by adaptation level theory, occurred when faces varied along the brightness or orientation dimension, but not for morphed faces. Changing the difficulty of discrimination of both training and test stimuli for Experiment 2 produced range effects in morphed faces. Experiment 3 explored training and testing stimulus factors as determinants of range effects in morphed faces. The results suggest that sufficiently biased testing ranges create shifts in response distributions (generalization gradients), and this may be amplified byusing relatively difficult discriminations between training stimuli.

Discrimination, Psychological↗

PubMed2005

Honeybees (Apis mellifera) holding on to memories: response competition causes retroactive interference effects.

Five experiments on honeybees examined how the learning of a second task interferes with what was previously learned. Free flying bees were tested for landmark-based memory in variations on a paradigm of retroactive interference. Bees first learned Task 1, were tested on Task 1 (Test 1), then learned Task 2, and were tested again on Task 1 (Test 2). A 60-min delay (waiting in a box) before Test 2 caused no performance decrements. If the two tasks had conflicting response requirements, (e.g., target right of a green landmark in Task 1 and left of a blue landmark in Task 2), then a strong decrement on Test 2 was found (retroactive interference effect). When response competition was minimised during training or testing, however, the decrement on Test 2 was small or nonexistent. The results implicate response competition as a major contributor to the retroactive interference effect. The honeybee seems to hold on to memories; new memories do not wipe out old ones.

Animals↗

PubMed2005

Age-related differences in heparin response.

INTRODUCTION: Major physiological differences in the coagulation system throughout childhood, compared to adults, are well documented. However, the impact of this on anticoagulant drugs is unknown. This study aimed to determine whether heparin therapeutic range determination is affected by the age of plasma donors and whether age-specific therapeutic ranges for heparin therapy may need to be considered in the clinical setting. MATERIALS AND METHODS: Plasma samples were obtained from healthy children and adults, and pooled into age-specific pools. These were spiked with different concentrations of heparin and APTT; Anti-Factor Xa and Anti-Factor IIa were measured using standard techniques. The experiments were repeated using three separate plasma pools, and results expressed as means with standard deviations. RESULTS AND CONCLUSIONS: The results show clear age-related differences in APTT for the same Anti-Factor Xa heparin concentration. The differences were more pronounced in younger children, with higher APTT for same Anti-Factor Xa. The Anti-Factor IIa activity of heparin for a given Anti-Factor Xa activity also differed between age-specific plasma pools. This study suggests that when using heparin in children, basic assumptions about the drug mechanism of action and implications for therapeutic ranges need to be considered.

Adolescent↗

PubMed2005

Shape parameters explain data from spatial transformations: comment on Pearce et al. (2004) and Tommasi & Polli (2004).

In 2 recent studies on rats (J. M. Pearce, M. A. Good, P. M. Jones, & A. McGregor, see record 2004-12429-006) and chicks (L. Tommasi & C. Polli, see record 2004-15642-007), the animals were trained to search in 1 corner of a rectilinear space. When tested in transformed spaces of different shapes, the animals still showed systematic choices. Both articles rejected the global matching of shape in favor of local matching processes. The present authors show that although matching by shape congruence is unlikely, matching by the shape parameter of the 1st principal axis can explain all the data. Other shape parameters, such as symmetry axes, may do even better. Animals are likely to use some global matching to constrain and guide the use of local cues; such use keeps local matching processes from exploding in complexity.

Animals↗

PubMed2005

Goldfish (Carassius auratus) matching geometric and featural cues: a reinterpretation of some of the data of Vargas, López, Salas, and Thinus-Blanc (2004).

Vargas, López, Salas, and Thinus-Blanc showed that goldfish (Carassius auratus) can use both geometric and featural cues in relocating a target corner in a rectangular enclosure. When featural cues (arrangement of striped walls) were put in conflict with geometric cues, results differed according to target location during training. Vargas, López, et al. explained the results of their cue conflict in terms of 2 different strategies: mapping and cue guidance. I provide an alternative, more parsimonious interpretation in which the same strategy of attempting to match as many cues as possible applies to both cases.

Animals↗

PubMed2005

Context cues eliminate retroactive interference effects in honeybees Apis mellifera.

Free flying honeybees were trained successively on two different tasks of landmark-based spatial memory. On both task 1 and task 2, the goal was at a consistent distance and direction from a cylindrical landmark. The colours of the landmarks differed for the two tasks. The target direction from the landmark in task 2 was opposite to that in task 1. The context in which task 2 took place was either the same as the task-1 context or different: being a short distance away, having different surrounding landmarks, and a different colour on the training table. After each task, the bees were tested on task 1 in the task-1 context (test 1 and test 2). If task 2 had the same context as task 1, the bees performed at chance on test 2. If task 2 had a different context, performance on test 2 was unaffected, remaining as good as on test 1. Contextual cues thus guide memory retrieval, and prevent any confusions about which response (that appropriate for task 1 or for task 2) to perform.

Animals↗

PubMed2005

Colouration in crab spiders: substrate choice and prey attraction.

Australian crab spiders Thomisus spectabilis ambush pollinating insects, such as honeybees (Apis mellifera) on flowers, and can change their body colour between yellow and white. It is traditionally assumed that the spiders change their colour to match the flower colour, thus rendering them cryptic to insect prey. Here, we test this assumption combining state-of-the-art knowledge of bee vision and behavioural experiments. In the field, yellow spiders are only found on yellow daisies (Chrysanthemum frutescens), whereas white spiders are found on yellow and white daisies. These field patterns were confirmed in the laboratory. When given the choice between white and yellow daisies, yellow spiders preferred yellow daisies, whereas white spiders showed only a slight but non-significant preference for white flowers. Thus, T. spectabilis select background colours according to their own body colour. When viewed from a distance, bees use an achromatic signal produced by their green receptors for target detection. Through this visual channel, white spiders on white flowers, and yellow spiders on yellow flowers are virtually undetectable. From a closer distance of a few centimetres, when bees evaluate colour contrast, the combination of spider colour against different flower backgrounds affected the response of honeybees, but not in ways predicted by a classical crypsis/conspicuousness interpretation. Yellow spiders on yellow flowers are not perfectly matched when interpreted through the colour vision of a honeybee. Nevertheless, honeybees showed indifference to the presence of a spider, equally landing on vacant or spider-occupied flowers. Likewise, white spiders are poorly hidden on white flowers, as white spiders reflect ultraviolet light strongly, while white flowers do not. Surprisingly, bees are attracted to this contrast, and significantly more honeybees preferred white flowers occupied by white spiders. White spiders on yellow flowers produce the highest colour contrast and bees again preferred spider-occupied flowers. Yellow spiders on white flowers were the only pairing where bees rejected spider-occupied flowers, especially in cases where the contrast between the two was relatively strong. Thus, T. spectabilis select flower colours adaptively in a way that deceives honeybees, or at least does not deter them.

Animals↗

PubMed2005

The role of UV in crab spider signals: effects on perception by prey and predators.

Australian crab spiders Thomisus spectabilis sit on the petals of flowers and ambush prey such as honeybees. White-coloured T. spectabilis reflect in the UV (UV+ spiders) and previous research has shown that their presence, curiously, attracts honeybees to daisies. We applied an UV-absorber (Parsol) to create UV-absorbing (UV-) spiders that did not reflect any light below 395 nm wavelength. These physical changes of visual signals generated by crab spiders caused honeybees to avoid flowers with UV- spiders on their petals. They also affected the perception of UV- spiders by honeybees and a potential avian predator (blue tits). Compared to UV+ spiders, UV- spiders produced less excitation of the UV-photoreceptors in honeybees and blue tits, which translated into a reduced UV-receptor contrast and a reduced overall colour contrast between UV- spiders and daisy petals. Our results reveal that a clean physical elimination of reflection in the UV range affects perception in predators and prey and ultimately changes the behaviour of prey.

Animals↗

PubMed2005

Is there a geometric module for spatial orientation? Squaring theory and evidence.

There is evidence, beginning with Cheng (1986), that mobile animals may use the geometry of surrounding areas to reorient following disorientation. Gallistel (1990) proposed that geometry is used to compute the major or minor axes of space and suggested that such information might form an encapsulated cognitive module. Research reviewed here, conducted on a wide variety of species since the initial discovery of the use of geometry and the formulation of the modularity claim, has supported some aspects of the approach, while casting doubt on others. Three possible processing models are presented that vary in the way in which (and the extent to which) they instantiate the modularity claim. The extant data do not permit us to discriminate among them. We propose a modified concept of modularity for which an empirical program of research is more tractable.

Adult↗

PubMed2002

Generalisation: mechanistic and functional explanations.

An overview of mechanistic and functional accounts of stimulus generalisation is given. Mechanistic accounts rely on the process of spreading activation across units representing stimuli. Different models implement the spread in different ways, ranging from diffusion to connectionist networks. A functional account proposed by Shepard analyses the probabilistic structure of the world for invariants. A universal law based on one such invariant claims that under a suitable scaling of the stimulus dimension, generalisation gradients should be approximately exponential in shape. Data from both vertebrates and invertebrates so far uphold Shepard's law. Some data on spatial generalisation in honeybees are presented to illustrate how Shepard's law can be used to determine the metric for combining discrepancies in different stimulus dimensions. The phenomenon of peak shift is discussed. Comments on mechanistic and functional approaches to generalisation are given.

Adaptation, Physiological↗

PubMed2002

Self-control in honeybees.

Self-control means choosing a large delayed reward over a small immediate reward; impulsiveness is its opposite. The metabolic hypothesis states that the amount of self-control across species correlates negatively with metabolic rate (Tobin & Logue, 1994). Foraging honeybees have high metabolic rates; the metabolic hypothesis would predict little self-control in bees. But foraging bees work for the long-term good of their hive, conditions that seem to require self-control. In three experiments, we gave bees the choice between (1) a sweeter delayed reward and a less sweet immediate reward and (2) a large delayed reward and a small immediate reward. Bees showed much self-control, inconsistent with the metabolic hypothesis.

Animals↗